The paper describes a phonetic experiment that dealt with the place assimilation of voiceless palatalised alveolar fricative /sj/ by following postalveolar alveo-palatal fricative /e:/ at word boundaries in Modern Standard Russian. As the former sibilant is commonly described as a geminated sound and Russian prohibits long consonants in positions near other consonants, the assimilation process can potentially lead to neutralisation in such minimal pairs of word combinations as proyavila shchedrost' [(she) showed generosity] and proyavilas' shchedrost' [generosity showed itself]. The participants of the experiment, 20 native Russian speakers (10 men and 10 women aged 18 to 40), were instructed to read a list of sentences that included 8 minimal pairs of target word combinations embedded in carrier phrases. All stimuli were recorded in intervocalic position; phrasal accent on stimuli was avoided; accent structure of the target word combinations was deliberately varied (clusters were recorded in all possible positions with regard to stressed and unstressed vowels). All recordings were analysed using computer software Praat. The duration and homogeneity of fricative noise were measured. Spectral analysis showed that in 78% of cases place assimilation of sibilants at word boundaries was complete. The measurements of duration confirmed that this parameter could vary widely, mostly in connection with stress. The duration of [e(:)] sounds within minimal pairs pronounced by the same speaker showed that in similar conditions in 95.5% of cases the sound representing the underlying /sj#e:/ was longer than the surface representation of the underlying /#e:/ (mean difference 34,9 ms; mean duration ratio 1,26). In order to find out whether these durational differences can be used by native speakers to distinguish minimal pairs a perception experiment was conducted. 15 native speakers, students aged 17-19, were presented with 35 stimuli (word consequences recorded during the described above experiment, but removed from phrasal context; the duration of the fricative varied widely from 135 to 202 ms). The participants' task was to write down what they think they heard. Their responses demonstrated that they could not reliably distinguish tokens with place assimilation of underlying /sj/ (the number of correct guesses was at a chance rate - 50.8%) and tokens without underlying /sj/ (the number of correct guesses was only slightly larger - 57.1%) despite the significant durational differences. The described phenomenon can be interpreted as a case of incomplete neutralisation. The experiments showed that the neutralisation of /#e:/ and /sj#e:/ at word boundaries in Russian is phonetically incomplete due to the significant durational differences between the produced fricatives, although these acoustic cues were not used by native speakers in distinguishing minimal pairs.